Light emitting module

A light emitting module comprising:

• a semiconductor laser;
• a collimating lens that collimates light beam output from the semiconductor laser in a beam spread state;
• a first prism pair including two triangular-plate-shaped prisms, each passing the light beam between two end surfaces on both sides of one apex angle to refract the light beam, and the prisms being sequentially arranged on an optical path of the collimated light beam in such a manner that the orientations of apex angles of the prisms are opposite to each other;
• a first rotary stage configured to hold the first prism pair and to be rotatable about a rotation axis extending in a prism thickness direction in such a manner that an incident angle of the collimated light beam entering a prism positioned on the upstream side of the optical path is changed;
• and
• two aperture plates;
• wherein each of the two aperture plates comprises a light-blocking member with a circular aperture formed therein to allow the passage of the parallel light, and blocks at least a portion of a return light which is emitted from the semiconductor laser, reflected externally, and then travels toward the semiconductor laser, and
• wherein the two aperture plates are arranged such that their positions along the direction of propagation of the reflected light are different from each other.